Abstract
In this study, a simple methodology for mapping the seasonal cultivated area of the Gash Delta Spate Irrigation System based on satellite images was developed. The methodology combined information from multiple bands to characterize the land surface in terms of spectral indices (e.g., Normalized Difference Vegetation Index (NDVI), and surface temperature (Ts)). Visual interpretations of a conveniently selected image were undertaken to identify and select sample points of interest. The NDVI and Ts values (computed from multi-date images that represented the crop growing period) of the sample points were used to developed typical NDVI and Ts plots. By analyzing these plots and the cropping calendar, an NDVI and Ts threshold-based algorithm was developed to extract the cultivated area of a given season. Analysis of the developed algorithm showed that it was simple, easily modifiable, and had interpretable rules and threshold values. Comparing the extracted cultivated area with the field report area showed a promising application of the methodology to map and estimate the cultivated area from only remote sensing data.
Highlights
As competition for water increases and commitments for sustainable ecosystems grow, an increasing awareness has been observed in recent times for making the best use of water, a scarce and valuable resource for all economic activities [1,2]
The Modified Normalized Difference Water Index (MNDWI) and Normalized Difference Vegetation Index (NDVI) enhanced the presence of water and vegetation, respectively
The pseudo natural color, MNDWI, and NDVI maps showed a distinction between the irrigated, bare-dry, and forest areas, information from standard false color and Google Earth were used to increase the confidence of identifying and selecting the sample points of interest
Summary
As competition for water increases and commitments for sustainable ecosystems grow, an increasing awareness has been observed in recent times for making the best use of water, a scarce and valuable resource for all economic activities [1,2]. Accurate information on irrigated agricultural water use, and its spatial extent and variation, is essential for water resource and crop productivity assessments [4]. One type of information that requires accurate estimation is the acreage of an irrigation system It is an important input parameter for many irrigation performance indicators such as water use, water productivity, water rights, impact assessment, and performance diagnosis, among others [5]. Despite their importance in estimating irrigation performance indicators, irrigation system data including irrigated/cultivated area are seldom measured in a regular and reliable manner to cover the entire irrigation system. According to [6], the lack of proper and effective management of irrigation systems is related to the conventional method of data collection through field observation, which is difficult, time-consuming, and inadequate in temporal and spatial coverage
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